1. Field of the Invention:
The invention relates to high filler content plastic molded articles which resemble granite, which articles are based on polymethyl methacrylate (PMMA) and contain decorative pigments.
2. Discussion of the Background:
High filler content plastic resins which resemble various rocks have been long known (see 1992, Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., Vol. A 20, pub. VCH, pp. 494-500).
In this connection, imitation marbles and granites have achieved particular industrial interest and importance.
Thus, Ger. Pat. 2,627,081 discloses an imitation granite based on irregular distribution of two discrete types of filler particles in a PMMA matrix, which particles are namely
(1) colored or colorless, non-translucent particles; and PA1 (2) colored or colorless, translucent or transparent particles; PA1 A) 80-20 parts by weight (pbw) of a liquid PMMA polymer precursor; PA1 B) 0-75, preferably 40-75 pbw of a (non-metallized) particulate filler; PA1 C) 0-5 pbw (based on the sum of A and B) of a polymerizable organosilicon compound, as an adhesion promoter; and PA1 D) 0-2 wt. % of one or more pigments or colorants; wherewith the aforesaid metallic-appearing particles are of a platelet-like stratified silicate (SS) in the particle size range 20-500 micron, used in the amount of 1-35 pbw (based on the sum of A and B); and wherewith the freeradical polymerization is carried out to completion. Preferably, the sum of A and B is 100 pbw. PA1 a large number of light-reflecting particles which are fixed at or near the surface but in a nonuniform arrangement, and PA1 similarly distributed pigment particles. Molded articles prepared by the present method also meet requirements for mechanical and wear characteristics, e.g. for application in health and sanitary applications, for use in kitchenware, use in decorative panels, and the like.
wherewith both types of particles have minimum particle size (taken as the minimum dimension) &gt;200 micron. An index of refraction n.sub.D of the PMMA material and the filler material of 1.4-1.6 is prescribed.
PCT OS WO 91/11,404 discloses an imitation granite which is colored and which is comprised of:
(i) a matrix containing PMMA and particles of aluminum oxide trihydrate, which particles are of length &lt;100 micron; (ii) PMMA particles in the 100-5,000 micron size range, filled with 50-70 wt. % of aluminum oxide trihydrate and up to 2.5 wt. % of a colorless-to-white pigment; (iii) PMMA particles in the 100-5,000 micron size range, filled with 0.1-2.5 wt. % black pigment; and (iv) PMMA particles in the 100-5,000 micron size range, filled with pigments of other colors. The tendency of the larger particles to settle is countered by the use of rheologically effective additives.
The teaching of PCT OS WO 90-01,470 (the same applicant as WO 91/11,404) is different as to the particle sizes and pigment(s).
Ger. OS 38 21 116 discloses colored polyacrylate plates with a stone appearance. The precursor of the matrix polymer is homogeneously colored. A pulverized acrylic resin, also colored but of a color different from that of the matrix polymer, is subsequently added and distributed into the matrix polymer. After conclusion of the polymerization, the molded articles in which the original pulverized acrylic resin has settled are removed from the mold. However, the existing methods of manufacturing molded plastic articles which resemble granite involve relatively complex systems and procedures.